As information industry rapidly progresses recently, a variety of information processing systems, and recording methods or apparatuses suitable for those information processing systems have been developed and employed. In such recording methods, ink recording using a jet for emitting ink or a plotter and thermal transfer recording using a melt type colorant or a sublimation type colorant employs apparatuses which are lightweight, compact-sized and noiseless and further excellent in operating properties and maintainability. Moreover, the apparatuses used in those recording methods can be easily modified to provide color recording, and hence those recording methods have been widely used in recent years. Also in the conventional electrophotographic recording method, full color printers and copying machines showing high resolving power have been developed and commercialized, while the color recording has progressed.
Recording methods for the ink-jet recording can be roughly classified into three methods: a method of using an aqueous dye solution of a water-soluble dye (aqueous ink), a method of using a dye solution obtained by dissolving an oil-soluble dye in an organic solvent (oily ink) and a method of using a molten low-temperature-melting solid wax containing a dye (wax ink). The method of using the aqueous ink is mainly adopted. In any of those methods, an image is formed by emitting the ink in the form of fine droplets onto a recording sheet.
The thermal transfer recording can be roughly classified into two methods: a first method of imagewise applying heat to an ink-sheet having a hot-melt ink coated on a support from the support side to melt the ink according to the pattern, and transferring the thus melted ink to a recording sheet to obtain an ink image (melt type thermal transfer method); and a second method of imagewise applying heat to an ink-sheet comprising a Support and a layer of a high-temperature-melting resin and a sublimation dye from the support side in the same manner as described in the first method to sublimate the sublimation dye according to the pattern, and transferring the dye thus sublimated to a recording sheet to obtain an image (sublimation type thermal transfer method).
In the electrophotographic recording, mainly employed is a method in which an light pattern is applied to an electrostatically charged photoconductive layer to form an electrostatic latent image, the latent image is developed with toner, the toner image is transferred to a recording sheet, and finally the toner image is melted and fixed on the recording sheet under heating. Such recording sheet is usually required to have excellent adhesion to toner and resistance to embossing (formation of uneven surface of the recording sheet produced when an image was copied on the recording sheet by the electrophotographic copying machine).
For OHP films which have been widely used for presentation in place of slides, films for back light display which have been widely used in place of printed posters or display boards, and intermediates (namely, prints which are used as a master for further production), the recording sheet is required to be transparent. Such transparent sheet usually comprises a transparent film and a colorant-receptive (absorbing) layer provided thereon. Also in the transparent sheet, an image is formed thereon as described above, so as to prepare an sheet having a transparency (an image fixed on a clear base especially adaptable for viewing by transmitted light).
An image which has been formed on the transparent film by these recording methods, is required to show not only excellent hue, saturation and lightness but also good adhesion between a colorant and the surface of the recording sheet. Moreover, the ink-jet recording needs the transparent film to rapidly absorb a liquid ink and not to allow bleeding or blooming of ink or forming of puddle of ink on the film, from the viewpoint of obtaining a clear image.
In order to solve those problems, various proposals have been made so far. As for the transparent sheet forming transparency, the proposals are as follows:
Japanese Patent Provisional Publications No. 57(1982)-14091 and No. 61(1986)-19389 disclose a recording sheet comprising a support and a transparent layer composed of colloidal silica and water-soluble resin. The transparent layer has a low void volume because the colloidal silica has a large particle size and the amount of water-soluble resin is large, compared with that of colloidal silica. Therefore, the recording sheet does not give a satisfactory ink absorption speed.
Further, a recording sheet having a colorant-receptive layer having fine pores which is formed of pseudo-boehmite fine particles is described in Japanese Patent Provisional Publications No. 2(1990)-276670 and No. 3(1991)-281383. According to the studies by the inventor, however, it has been confirmed that sufficient transparency cannot be obtained by this recording sheet because of its high refractive index of about 1.65, though the ink absorption properties are satisfactorily improved.
Japanese Patent Publication No. 61(1986)-53958 discloses a recording sheet comprising a support and a transparent layer composed of synthetic silica, a fine inorganic particle of refractive index of 1.44-1.55 and water-soluble resin. The synthetic silica usually has a mean primary particle diameter of more than 10 nm, and further contains secondary particles having size of several hundreds nm. Therefore, the secondary particles are apt to scatter light applied thereto, whereby the recording sheet containing the particles does not show a satisfactory light transmittance. Further, the transparent layer has relatively large pores due to the large secondary particles and hence does not satisfactorily prevent occurrence of bleeding or blooming of ink.